Materials for near field transducers, near field tranducers containing same, and methods of forming

ABSTRACT

A device including a near field transducer, the near field transducer including gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two other secondary atoms, the at least two other secondary atoms selected from: boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), nitrogen (N), oxygen (O), carbon (C), antimony (Sb), gadolinium (Gd), samarium (Sm), thallium (Tl), cadmium (Cd), neodymium (Nd), phosphorus (P), lead (Pb), hafnium (Hf), niobium (Nb), erbium (Er), zinc (Zn), magnesium (Mg), palladium (Pd), vanadium (V), zinc (Zn), chromium (Cr), iron (Fe), lithium (Li), nickel (Ni), platinum (Pt), sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), beryllium (Be), thulium (Tm), erbium (Er), ytterbium (Yb), promethium (Pm), neodymium (Nd cobalt (Co), cerium (Ce), lanthanum (La), praseodymium (Pr), or combinations thereof.

PRIORITY

This application claims priority to U.S. Provisional Application Nos. 61/838,405 entitled “NEAR FIELD TRANSDUCER MATERIALS” filed on Jun. 24, 2013, 61/838,393 entitled “MATERIALS FOR NEAR FIELD TRANSDUCERS AND NEAR FIELD TRANSDUCERS INCLUDING THE SAME” filed on Jun. 24, 2013, 61/897,303 entitled “MATERIALS FOR NEAR FIELD TRANSDUCERS AND NEAR FIELD TRANSDUCERS INCLUDING THE SAME” filed on Oct. 30, 2013, 61/838,398 entitled “NEAR FIELD TRANSDUCERS AND METHODS OF FORMING THE SAME” filed on Jun. 24, 2013, 61/838,626 entitled “NEAR FIELD TRANSDUCERS AND METHODS OF FORMING THE SAME” filed on Jun. 24, 2013, and 61/984,915 entitled “METHODS OF FORMING NEAR FIELD TRANSDUCERS(NFTS) USING ION IMPLANTATION” filed on Apr. 28, 2014, the disclosure of which is incorporated herein by reference thereto.

SUMMARY

A device including a near field transducer, the near field transducer including gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two other secondary atoms, the at least two other secondary atoms selected from: boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), nitrogen (N), oxygen (O), carbon (C), antimony (Sb), gadolinium (Gd), samarium (Sm), thallium (Tl), cadmium (Cd), neodymium (Nd), phosphorus (P), lead (Pb), hafnium (Hf), niobium (Nb), erbium (Er), zinc (Zn), magnesium (Mg), palladium (Pd), vanadium (V), zinc (Zn), chromium (Cr), iron (Fe), lithium (Li), nickel (Ni), platinum (Pt), sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), beryllium (Be), thulium (Tm), erbium (Er), ytterbium (Yb), promethium (Pm), neodymium (Nd cobalt (Co), cerium (Ce), lanthanum (La), praseodymium (Pr), or combinations thereof.

A device including a light source; a waveguide; and a near field transducer, the near field transducer including gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two other secondary atoms, the at least two other secondary atoms selected from: boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), nitrogen (N), oxygen (O), carbon (C), antimony (Sb), gadolinium (Gd), samarium (Sm), thallium (Tl), cadmium (Cd), neodymium (Nd), phosphorus (P), lead (Pb), hafnium (Hf), niobium (Nb), erbium (Er), zinc (Zn), magnesium (Mg), palladium (Pd), vanadium (V), zinc (Zn), chromium (Cr), iron (Fe), lithium (Li), nickel (Ni), platinum (Pt), sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), beryllium (Be), thulium (Tm), erbium (Er), ytterbium (Yb), promethium (Pm), neodymium (Nd cobalt (Co), cerium (Ce), lanthanum (La), praseodymium (Pr), or combinations thereof.

A disc drive including at least one actuator arm having a first and a second end; at least one head, wherein each arm has a head at the first end thereof and wherein each head includes: a light source; a near field transducer, the near field transducer including gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two other secondary atoms, the at least two other secondary atoms selected from: boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), nitrogen (N), oxygen (O), carbon (C), antimony (Sb), gadolinium (Gd), samarium (Sm), thallium (Tl), cadmium (Cd), neodymium (Nd), phosphorus (P), lead (Pb), hafnium (Hf), niobium (Nb), erbium (Er), zinc (Zn), magnesium (Mg), palladium (Pd), vanadium (V), zinc (Zn), chromium (Cr), iron (Fe), lithium (Li), nickel (Ni), platinum (Pt), sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), beryllium (Be), thulium (Tm), erbium (Er), ytterbium (Yb), promethium (Pm), neodymium (Nd cobalt (Co), cerium (Ce), lanthanum (La), praseodymium (Pr), or combinations thereof; a magnetic reader; and a magnetic writer, wherein the light source and the near field transducer are configured to transmit light from the light source to the near field transducer in order to assist the magnetic writer with writing.

The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a pictorial representation of a data storage device in the form of a disc drive that can include a recording head constructed in accordance with an aspect of this disclosure.

FIG. 2 is a side elevation view of a recording head constructed in accordance with an aspect of the invention.

FIG. 3 is a schematic representation of a near field transducer.

FIG. 4 is a schematic representation of another near field transducer.

FIG. 5 shows the total energies of the grain boundary with the boron atom in the bulk interstitial site and in the grain boundary hollow site with respect to expansion distances of the cell.

FIG. 6 shows a graph comparing the experimental T and C_(o) ranges with calculated positions of T_(B) and T_(C) for Pb—In—Sn and Bi—In—Sn grain growth.

FIG. 7 shows the relative atomic size difference versus the grain boundary segregation energy of various elements.

FIG. 8 shows the enthalpy of mixing vs enthalpy of grain boundary segregation for alloying elements in a silver matrix.

FIGS. 9A, 9B, and 9C show the relative atomic size difference versus the grain boundary segregation energy of various elements.

FIG. 10 shows the enthalpy of mixing vs enthalpy of grain boundary segregation for alloying elements in a copper matrix.

FIG. 11 shows the enthalpy of mixing vs enthalpy of grain boundary segregation for alloying elements in an aluminum matrix.

The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

DETAILED DESCRIPTION

Heat assisted magnetic recording (referred to through as HAMR) utilizes radiation, for example from a laser, to heat media to a temperature above its curie temperature, enabling magnetic recording. In order to deliver the radiation, e.g., a laser beam, to a small area (on the order of 20 to 50 nm for example) of the medium, a NFT is utilized. During a magnetic recording operation, the NFT absorbs energy from a laser and focuses it to a very small area; this can cause the temperature of the NFT to increase. The temperature of the NFT can be elevated up to about 400° C. or more.

The very high temperatures that the NFT reaches during operation can lead to diffusion of the material of the NFT (for example gold) from the peg and towards the disk. In addition, a portion of the NFT may be exposed at the air bearing surface of the recording head and is thus subject to mechanical wearing. NFT performance is greatly influenced by the heat and mechanical stress during HAMR operation. It would therefore be advantageous to have NFT devices that are more durable.

Disclosed devices can offer the advantage of providing more efficient transfer of energy from an energy source to the magnetic storage media to be heated, a smaller focal point at the point of heating, or some combination thereof. In some embodiments, disclosed devices can be used within other devices or systems, such as magnetic recording heads, more specifically, thermally or heat assisted magnetic recording (HAMR) heads, or disc drives that include such devices.

Disclosed herein are NFTs and devices that include such NFTs. FIG. 1 is a pictorial representation of a data storage device in the form of a disc drive 10 that can utilize disclosed NFTs. The disc drive 10 includes a housing 12 (with the upper portion removed and the lower portion visible in this view) sized and configured to contain the various components of the disc drive. The disc drive 10 includes a spindle motor 14 for rotating at least one magnetic storage media 16 within the housing. At least one arm 18 is contained within the housing 12, with each arm 18 having a first end 20 with a recording head or slider 22, and a second end 24 pivotally mounted on a shaft by a bearing 26. An actuator motor 28 is located at the arm's second end 24 for pivoting the arm 18 to position the recording head 22 over a desired sector or track 27 of the disc 16. The actuator motor 28 is regulated by a controller, which is not shown in this view and is well-known in the art. The storage media may include, for example, continuous media or bit patterned media.

For heat assisted magnetic recording (HAMR), electromagnetic radiation, for example, visible, infrared or ultraviolet light is directed onto a surface of the data storage media to raise the temperature of a localized area of the media to facilitate switching of the magnetization of the area. Recent designs of HAMR recording heads include a thin film waveguide on a slider to guide light toward the storage media and a near field transducer to focus the light to a spot size smaller than the diffraction limit. While FIG. 1 shows a disc drive, disclosed NFTs can be utilized in other devices that include a near field transducer.

FIG. 2 is a side elevation view of a recording head that may include a disclosed NFT; the recording head is positioned near a storage media. The recording head 30 includes a substrate 32, a base coat 34 on the substrate, a bottom pole 36 on the base coat, and a top pole 38 that is magnetically coupled to the bottom pole through a yoke or pedestal 40. A waveguide 42 is positioned between the top and bottom poles. The waveguide includes a core layer 44 and cladding layers 46 and 48 on opposite sides of the core layer. A mirror 50 is positioned adjacent to one of the cladding layers. The top pole is a two-piece pole that includes a first portion, or pole body 52, having a first end 54 that is spaced from the air bearing surface 56, and a second portion, or sloped pole piece 58, extending from the first portion and tilted in a direction toward the bottom pole. The second portion is structured to include an end adjacent to the air bearing surface 56 of the recording head, with the end being closer to the waveguide than the first portion of the top pole. A planar coil 60 also extends between the top and bottom poles and around the pedestal. In this example, the top pole serves as a write pole and the bottom pole serves as a return pole.

An insulating material 62 separates the coil turns. In one example, the substrate can be AlTiC, the core layer can be Ta₂O₅, and the cladding layers (and other insulating layers) can be Al₂O₃. A top layer of insulating material 63 can be formed on the top pole. A heat sink 64 is positioned adjacent to the sloped pole piece 58. The heat sink can be comprised of a non-magnetic material, such as for example Au.

As illustrated in FIG. 2, the recording head 30 includes a structure for heating the magnetic storage media 16 proximate to where the write pole 58 applies the magnetic write field H to the storage media 16. In this example, the media 16 includes a substrate 68, a heat sink layer 70, a magnetic recording layer 72, and a protective layer 74. However, other types of media, such as bit patterned media can be used. A magnetic field H produced by current in the coil 60 is used to control the direction of magnetization of bits 76 in the recording layer of the media.

The storage media 16 is positioned adjacent to or under the recording head 30. The waveguide 42 conducts light from a source 78 of electromagnetic radiation, which may be, for example, ultraviolet, infrared, or visible light. The source may be, for example, a laser diode, or other suitable laser light source for directing a light beam 80 toward the waveguide 42. Specific exemplary types of light sources 78 can include, for example laser diodes, light emitting diodes (LEDs), edge emitting laser diodes (EELs), vertical cavity surface emitting lasers (VCSELs), and surface emitting diodes. In some embodiments, the light source can produce energy having a wavelength of 830 nm, for example. Various techniques that are known for coupling the light beam 80 into the waveguide 42 may be used. Once the light beam 80 is coupled into the waveguide 42, the light propagates through the waveguide 42 toward a truncated end of the waveguide 42 that is formed adjacent the air bearing surface (ABS) of the recording head 30. Light exits the end of the waveguide and heats a portion of the media, as the media moves relative to the recording head as shown by arrow 82. A near-field transducer (NFT) 84 is positioned in or adjacent to the waveguide and at or near the air bearing surface. The heat sink material may be chosen such that it does not interfere with the resonance of the NFT.

Although the example of FIG. 2 shows a perpendicular magnetic recording head and a perpendicular magnetic storage media, it will be appreciated that the disclosure may also be used in conjunction with other types of recording heads and/or storage media where it may be desirable to concentrate light to a small spot.

FIG. 3 is a schematic view of a lollypop NFT 90 in combination with a heat sink 92. The NFT includes a disk shaped portion 94 and a peg 96 extending from the disk shaped portion. The heat sink 92 can be positioned between the disk shaped portion and the sloped portion of the top pole in FIG. 2. When mounted in a recording head, the peg may be exposed at the ABS and thus can be subjected to mechanical wearing.

FIG. 4 is a schematic view of a coupled nanorod (CNR) NFT 100. This NFT includes two nanorods 102 and 104 separated by a gap 106. Nanorod 102 includes a first portion 108 and a second portion 110. Nanorod 104 includes a first portion 112 and a second portion 114. When mounted in a recording head, the ends 116 and 118 of the nanorods may be exposed at the ABS and thus be subject to mechanical wearing. FIGS. 3 and 4 show example NFTs. However, the disclosure is not limited to any particular type of NFT. The materials described below may be used in various NFT configurations.

Disclosed NFTs may be made of a primary atom and at least one secondary atom. In some embodiments, the primary atom may have a higher atomic percentage (at %) in the NFT. In some embodiments, the primary atom may be gold (Au). In some embodiments, more than one secondary atom is included in a NFT. A secondary atom(s) may be chosen by considering one or more properties of a material, mechanisms of atomic diffusion, or combinations thereof.

It is thought that, atoms, for example gold atoms diffuse through defects in the NFT. In solids, there are three kinds of defects: point defects (atoms missing, lattice vacancies, substitutional, interstitial impurities, and self-interstitials); linear defects (screw and edge dislocations); and planar defects (large angle and small angle grain boundaries, stacking faults, and external surfaces). Each type of defect provides its own mechanism for diffusion. As a result, there are three major mechanisms by which a NFT material (e.g., gold) may diffuse from the peg to the disk, namely, bulk or lattice diffusion, defect diffusion, and surface diffusion.

Bulk or lattice diffusion generally involves vacancy-atom exchange. It is by this process that the atoms in the layers intermingle so that the latter become of increasingly similar composition while totally in the solid state. Bulk diffusion is highly temperature dependent, and has a relatively small diffusion coefficient at temperatures below the melting point of the material.

The second mechanism is that of rapid diffusion along defect paths. This process is less dependent on temperature than is lattice diffusion and usually becomes dominant at lower temperatures. Defects like grain boundaries, dislocations and twin boundaries, which are common and practically unavoidable in metals, can serve as rapid transport pipes through a metallic layer.

The third mechanism is surface or interface diffusion. Due to the mismatch, there are high density defects at the surface and/or interface between the NFT and the surrounding CNS, NPS, and HOC. As a result, NFT atoms, e.g., gold atoms, have a relatively high diffusion coefficient through surface and/or interface diffusion.

Disclosed secondary atoms to combine with a primary atom may be chosen, at least in part, by keeping these diffusion mechanisms in mind. Various properties that may be considered then can include, for example bond energy/strength of the secondary atoms to the primary atom in comparison to the bond energy/strength of the primary atom to the primary atom, solubility of the secondary atom in the primary atom, size of the atomic radius, optical properties, oxidation resistance, melting point, or some combination thereof.

In some embodiments, at least one of the secondary atoms has a higher bond energy/strength than does the primary atom—primary atom bond. Such an atom may serve to reduce the primary material atom diffusion from the peg to the disk and thereby increase peg reliability. By considering, as an example, gold as the primary atom, the following can explain the effect of the bond energy/strength consideration. Gold has a face centered cubic (fcc) structure. In a gold lattice, each gold atom is bonded to the atoms at the 6 corners and 12 atoms at the center of the face, which means that one gold atom is connected to 18 other gold atoms. Potentially, adding one other atom with a high bond strength with gold could therefore affect the movement of 18 gold atoms. Due to the larger bond strength, it is expected that this atom will bond to the surrounding gold atoms and form atom clusters. This could prevent the separation of the gold atoms from the grain, which limits the source of free gold atoms. Also, the cluster could pin the defects, such as dislocations, small angle grain boundaries, and large angle grain boundary, which could obstruct movement of the defects, and therefore, hinder the gold diffusion. Furthermore, the unbound secondary atoms at the interface, the grain boundary, the dislocation, and other defects could attract the free gold atoms, which could further hinder transportation of the gold atoms through defect channels and thereby increase the NFT stability.

The existence of the secondary atom(s) on the NFT surface and at the NFT/surrounding material interfaces could also block the primary atom diffusion through surfaces and interfaces. Especially in circumstances, when the free primary atoms on the surface or at the interface diffuse away, leaving a relatively high concentration of secondary atoms on the surface or at the interface, which could prevent the further diffusion of the remaining primary atoms and increase the peg stability.

In some embodiments, the bond energy/strength of a secondary atom to the primary atom in comparison to the bond energy/strength of the primary atom to the primary atom may be relevant when considering elements to include as a secondary atom(s). Table 1 below shows bond dissociation energies of different atoms with gold. The bond dissociation energy of a bond indicates the bond energy/strength of a bond. The higher the bond dissociation energy, the stronger the bond is.

TABLE 1 Bond dissociation energy (kJ/mol) Bond Energy Bond Energy Bond Energy Bond (kJ/mol) Bond (kJ/mol) Bond (kJ/mol) Ag—Au 203 Al—Au 326 Au—Au 224.7 Au—B 367.8 Au—Ba 254.8 Au—Be 285 Au—Bi 297 Au—Ca 243 Au—Ce 339 Au—Cl 343 Au—Co 222 Au—Cr 213 Au—Cs 255 Au—Cu 228 Au—D 318 Au—Dy 259 Au—Eu 241 Au—F 294 Au—Fe 187 Au—Ga 234 Au—Ge 274.1 Au—H 292 Au—Ho 267 Au—I 276 Au—In 286 Au—La 336.4 Au—Li 284.5 Au—Lu 332 Au—Mg 243 Au—Mn 185.4 Au—Na 215 Au—Nd 299.2 Au—Ni 255 Au—O 221.8 Au—Pb 130 Au—Pd 155 Au—Pr 310 Au—Rb 243 Au—Rh 231 Au—S 418 Au—Sc 280 Au—Se 243 Au—Si 305.4 Au—Sn 254.8 Au—Sr 264 Au—Tb 289 Au—Te 317.6 Au—U 318 Au—V 240.6 Au—W 207.9 Au—Y 307.1

In some embodiments, the secondary atom can be boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), or combinations thereof, for example. In some embodiments, the secondary atom can be holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), or combinations thereof, for example. In some embodiments, the secondary atom can be barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), or combinations thereof, for example. In some embodiments, the secondary atom can be boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), or combinations thereof, for example.

In some embodiments, the solubility of the secondary atom in the primary atom may be relevant when considering elements to include as a secondary atom(s). If a secondary atom(s) has a relatively low solubility in the primary atom, the secondary atom(s) will exist mainly in the defects of the structure of the primary atoms. This can serve to reduce the diffusion of the gold atoms through the defects. In some embodiments, the secondary atom can be boron (B), bismuth (Bi), sulfur (S), silicon (Si), carbon (C), antimony (Sb), tellurium (Te), or combinations thereof, for example. In some embodiments, the secondary atom can be boron (B), bismuth (Bi), sulfur (S), silicon (Si), tellurium (Te), or combinations thereof, for example. In some embodiments, the secondary atom can be holmium (Ho), erbium (Er), lutetium (Lu), praseodymium (Pr), uranium (U), or combinations thereof, for example. In some embodiments, the secondary atom can be cesium (Cs), dysprosium (Dy), europium (Eu), gadolinium (Gd), germanium (Ge), rubidium (Rb), selenium (Se), samarium (Sm), terbium (Tb), thallium (Th), or combinations thereof, for example. In some embodiments, the secondary atom can be cesium (Cs), dysprosium (Dy), europium (Eu), germanium (Ge), rubidium (Rb), selenium (Se), terbium (Tb), or combinations thereof, for example. In some embodiments, the secondary atom can be boron (B), bismuth (Bi), sulfur (S), silicon (Si), carbon (C), antimony (Sb), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), uranium (U), cesium (Cs), dysprosium (Ds), europium (Eu), gadolinium (Gd), germanium (Ge), rubidium (Rb), selenium (Se), samarium (Sm), terbium (Tb), thallium (Th), cadmium (Cd), neodymium (Nd), phosphorus (P), lead (Pb), or combinations thereof, for example.

In some embodiments, atoms with high solubility in gold can have advantageous effects, while in some other embodiments, atoms with low solubility in gold can have advantageous effects. In some embodiments, only insoluble atoms can be added to a primary material so that the atoms stay in the defects. In some embodiment, only soluble atoms can be added to a primary material in order to increase the thermal stability of the primary material. In some embodiments, both soluble and insoluble atoms can be added to a primary material in order to increase the thermal stability of the primary material. In some embodiments, a combination of atoms with low solubility and atoms with high solubility may have an advantageous effect of improving the thermal stability of a primary material.

In some embodiments at least two secondary atoms can be included with a primary atom to form a NFT. In some such embodiments, a first secondary atom can include an element that has a relatively low solubility with the primary atom. In embodiments where the primary atom is gold, the secondary atoms listed in the preceding paragraph can be utilized in this embodiment. The second secondary atom in such an embodiment may have a relatively high solubility in the primary atom (e.g., gold) so that the second secondary atoms are distributed uniformly in the grains of the primary atoms. This may serve to prevent the primary atoms from leaving the grain. This could then eliminate the source of free gold atoms and block the diffusion of gold atoms through defects such as dislocations, interfaces, surfaces, grain boundaries, twin boundaries, or combinations thereof. In some such embodiments, the second secondary atom can be indium (In), tin (Sn), hafnium (Hf), niobium (Nb), manganese (Mn), or some combination thereof, for example. In some such embodiments, the second secondary atom can be erbium (Er), scandium (Sc), zinc (Zn), or some combination thereof, for example. In some such embodiments, the second secondary atom can be indium (In), tin (Sn), hafnium (Hf), niobium (Nb), manganese (Mn), erbium (Er), scandium (Sc), zinc (Zn), or some combination thereof, for example. In some embodiments, the second secondary atoms can be silver (Ag), copper (Cu), magnesium (Mg), palladium (Pd), vanadium (V), zinc (Zn), chromium (Cr), iron (Fe), lithium (Li), nickel (Ni), platinum (Pt), scandium (Sc), or some combination thereof, for example. It should also be noted that the atoms noted as second secondary atoms can also be used in combination with a primary material without the first secondary atom, e.g., a NFT can include only a primary material and a secondary material from the above noted second secondary atoms.

In some embodiments, secondary atom(s) can be chosen based on their atomic radii. In some embodiments, secondary atom(s) can be those that have larger atomic radii than the primary atom so that the secondary atom(s) have a low diffusion rate into the primary metal. Table 2 shows the atomic radii of a number of atoms.

TABLE 2 Atomic Symbol radius H 0.046 Li 0.152 Be 0.114 Be 0.097 C 0.077 N 0.071 O 0.06 Na 0.186 Mg 0.16 Al 0.143 Si 0.117 P 0.109 S 0.106 Cl 0.107 K 0.231 Ca 0.197 Sc 0.16 Ti 0.147 V 0.132 Pd 0.137 Ag 0.144 Cd 0.15 In 0.157 Sn 0.158 Sb 0.161 Te 0.143 In 0.136 Cs 0.265 Ba 0.217 La 0.187 Ce 0.182 Pr 0.183 Nd 0.182 Sm 0.181 Eu 0.204 Gd 0.18 Tb 0.177 Dy 0.177 Cr 0.125 Mn 0.112 Fe 0.124 Co 0.125 Ni 0.125 Cu 0.128 Zn 0.133 Ga 0.135 Ge 0.122 As 0.125 Se 0.116 Rb 0.251 Sr 0.215 Y 0.181 Zr 0.158 Nb 0.143 Mo 0.136 Ru 0.134 Rh 0.134 Ho 0.176 Er 0.175 Tm 0.174 Yb 0.193 Lu 0.173 Hf 0.159 Ta 0.147 W 0.137 Re 0.138 Os 0.135 Ir 0.135 Pt 0.138 Au 0.144 Hg 0.15 Tl 0.171 Pb 0.175 Bi 0.182 Th 0.18 U 0.138

In some embodiments, the secondary atom(s) can be bismuth (Bi), indium (In), tin (Sn), hafnium (Hf), niobium (Nb), antimony (Sb), tellurium (Te), or some combination thereof, for example. In some embodiments, the secondary atom(s) can be erbium (Er), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), or some combination thereof, for example. In some embodiments, the secondary atom(s) can be barium (Ba), cesium (Cs), dysprosium (Dy), europium (Eu), gadolinium (Gd), samarium (Sm), terbium (Tb), thallium (Th), or some combination thereof, for example.

In some embodiments, two secondary atoms can be utilized, a first secondary atom that has a low solubility in the primary atom and a second secondary atoms that has a high solubility in gold. In such embodiments, the first secondary atom (that have a low solubility in the primary atom) may reduce the diffusion of the primary atoms through defects, such as dislocations and grain boundaries, and the second secondary atoms (that have a high solubility in the primary atom) may reduce the diffusion of the primary atoms through lattice and surface/interface interactions.

In some embodiments, the first secondary atom (that has a low solubility in the primary atom) may be boron (B), bismuth (Bi), sulfur (S), silicon (Si), carbon (C), antimony (Sb), tellurium (Te), or combinations thereof, for example. In some embodiments, the first secondary atom can be boron (B), bismuth (Bi), sulfur (S), silicon (Si), tellurium (Te), or combinations thereof, for example. In some embodiments, the first secondary atom can be holmium (Ho), lutetium (Lu), praseodymium (Pr), uranium (U), or combinations thereof, for example. In some embodiments, the first secondary atom can be cesium (Cs), dysprosium (Dy), europium (Eu), gadolinium (Gd), germanium (Ge), rubidium (Rb), selenium (Se), samarium (Sm), terbium (Tb), thallium (Th), or combinations thereof, for example. In some embodiments, the first secondary atom can be cesium (Cs), dysprosium (Dy), europium (Eu), germanium (Ge), rubidium (Rb), selenium (Se), terbium (Tb), or combinations thereof, for example. In some embodiments, the first secondary atom can be boron (B), bismuth (Bi), sulfur (S), silicon (Si), carbon (C), antimony (Sb), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), uranium (U), cesium (Cs), dysprosium (Ds), europium (Eu), gadolinium (Gd), germanium (Ge), rubidium (Rb), selenium (Se), samarium (Sm), terbium (Tb), thallium (Th), or combinations thereof, for example.

In some embodiments, the second secondary atom can be indium (In), tin (Sn), hafnium (Hf), niobium (Nb), manganese (Mn), or some combination thereof, for example. In some such embodiments, the second secondary atom can be erbium (Er), scandium (Sc), zinc (Zn), or some combination thereof, for example. In some such embodiments, the second secondary atom can be indium (In), tin (Sn), hafnium (Hf), niobium (Nb), manganese (Mn), erbium (Er), scandium (Sc), zinc (Zn), or some combination thereof, for example. In some embodiments, the second secondary atom can be silver (Ag), copper (Cu), magnesium (Mg), palladium (Pd), vanadium (V), zinc (Zn), aluminum (Al), chromium (Cr), iron (Fe), nickel (Ni), lithium (Li), platinum (Pt), scandium (Sc), tantalum (Ta), or some combination thereof, for example.

In some embodiments, a NFT can also include a third secondary atom. In some embodiments, the third secondary atom can be one where the bond energy/strength of the third secondary atom-third secondary atom bond is less than that of the third secondary atom-primary atom bond so that the third secondary atom tends to bond to the primary atom instead of other third secondary atoms. As a result, the third secondary atoms may be substantially uniformly distributed in the primary atoms, which can increase the obstruction efficiency of the third secondary atoms.

In some embodiments, the secondary atom(s) can also be chosen by considering optical properties of the atoms or a material that includes the atoms (e.g., an alloy containing the primary atom and the secondary atom(s)). In some embodiments, atoms useful in a NFT can have optical properties that enable efficient coupling of incident light to the surface plasmons and effective energy transfer to the magnetic medium. The optical properties of NFT materials are often characterized by their optical refractive index (n) and extinction coefficient (k) which can be measured by ellipsometry. From the n and k values, the real and imaginary part of the dielectric constant (permittivity) can be calculated by: ∈₁=n²−k² and ∈₂=2nk. The plasmonic effect arises from the negative real part of the dielectric constant of the material. The strength of plasmonic coupling depends on the absolute value of ∈₁. On the other hand, the surface plasmon mode needs to propagate over a substantial distance. The loss of this propagation is proportional to the imaginary part of the dielectric ∈₂. A good plasmonic material will have high |∈₁| and low ∈₂. Hence a figure-of-merit (FOM) has been developed to characterize the “goodness” of plasmonic materials: FOM=3*|∈₁/∈₂|.

The near field transducers described above can be fabricated using a variety of techniques, including for example: sputtering from an alloy target; co-sputtering from multiple targets; reactive sputtering from an alloy target; reactive co-sputtering from multiple targets; co-evaporation from multiple sources; reactive co-evaporation from multiple sources; ion beam deposition from an alloy target; codeposition in electrochemical ways, including electroless deposition, electrodeposition, displacement reaction, chemical reduction, or electrophoretic deposition.

In some embodiments, secondary atom(s) can be chosen based on other considerations. For example, secondary atom(s) can be chosen based on mechanistic considerations involved in pinning grain growth. The NFT grain and interface boundary can be atomically engineered by the preferential adsorption of secondary atom(s) in order to pin the grain boundary and improve the grain boundary migration resistance of a NFT that includes, a primary atoms, such as gold for example. This can also be described as utilizing minor alloying elements (e.g., secondary atom(s)) to alter the fundamental grain boundary migration kinetics of the primary atom (e.g., gold). Mechanical high temperature reliability of the NFT may therefore be improved by intentional microalloying additions of one or more secondary atom(s) into the NFT material. Such intentional alloying can pin the grain boundary movement by the so called “solute drag” effect, making it harder for the peg to recess.

Disclosed concepts may provide stable NFT element dimensions during operating temperatures by pinning grain growth. This concept utilizes the preferential placement of secondary atoms at the grain boundaries of the NFT material to pin grain movement. The secondary atoms are chosen such that the total strain energy and total chemical potential energy of the system of atoms is reduced when they are at the grain boundary. Thus the grain boundary secondary atom is in a potential “well” and therefore “locks” the movement of the grain boundary.

The preferential placement of secondary atoms can be accomplished by facilitating the movement of secondary atoms to the grain boundaries. Such secondary atoms may be able to stabilize the NFT against grain growth through the following mechanisms: increased drag force on the moving grain boundary due to the binding chemical potential and elastic strain interaction of secondary atom to the grain boundary; reduction of grain boundary diffusion by poisoning of the primary atom (e.g., gold) grain boundary by the tightly adsorbed secondary atoms blocking of the diffusion jump sites at the boundary by the secondary atoms; reduction of the efficiency of secondary atom transfer across the grain boundary by the secondary atom; change in the grain boundary structure brought about by the secondary atom; preferential formation of vacancy-secondary atom pairs and secondary atom-primary atom pairs at the grain boundary which make boundary migration harder; improving the grain boundary cohesion; or some combination thereof.

The selection of the secondary atom can be based, at least in part on considerations involving the energetics of segregation of the secondary atom to the grain boundary. One consideration is the size of the secondary atom. In some embodiments the size of the secondary atom can be less than the size of the primary atom. If such a relationship exists the secondary atom can occupy interstitial positions in the bulk and at the grain boundary. In a face centered cubic (FCC) structure, the octahedral site is the largest interstitial site. FIG. 5 shows the total energies of the grain boundary with the boron atom in the bulk interstitial site and in the grain boundary hollow site with respect to expansion distances of the cell. By comparing the energetics of a grain boundary with a boron atom in the interstitial site, a grain boundary with hollow sites, and a pure aluminum grain boundary it can be seen that the boron atom does not expand the grain boundary hollow site. In fact the boron atom fits neatly into the grain boundary. The segregation energy is the difference in the total energy of the system with the boron atom in the grain boundary hollow site and the total energy of the grain boundary system with the boron atom in the bulk interstitial site. The driving force between the bulk and the grain boundary configuration is, in effect segregation energy. A negative segregation energy would enhance the grain boundary cohesion.

The same basic mechanism allows the secondary atom to poison the grain boundary/surface diffusivity. Secondary atoms having smaller radii may be more amenable to providing this effect. Grain boundary precipitants may also be formed based on the energetics of the system. From a consideration of this effect, boron (B), carbon (C), nitrogen (N), oxygen (O), or some combination thereof may be useful as a secondary atom(s).

It should be understood, having read this disclosure, that grain boundaries as discussed herein include high angle and low angle grain boundaries, coherent and incoherent boundaries, tilt and twist boundaries, intergranular phases as well as high symmetry boundaries such as twin boundaries.

An important consequence of these considerations is that NFTs without secondary atom(s) will have higher grain boundary mobilities and lower stabilities. Thus NFTs as typically formulated will have lower resistance to grain boundary movement since, by definition, they do not have secondary atoms in the system that can preferentially locate to the grain boundary. They will therefore possess undesirable grain migration and reliability performance.

In contrast, disclosed NFTs can utilize a secondary atom(s) to pin the grain boundary. A secondary atom(s) present even at a few 10s or 100s of ppm may make a dramatic impact in curtailing the mobility of the grain boundaries. Secondary atom(s) which reduce the strain energy and chemical potential at the grain boundary may lead to preferential clustering of secondary atoms near the grain boundaries (called Cottrell atmospheres) which may provide locking mechanisms that impede grain boundary movement. It should be emphasized that the primary function of the secondary atom(s) is grain boundary mobility impairment, although other functions such as solid solution strengthening are also possible.

A secondary atom can be chosen based, at least in part, on the ability for preferential segregation of the secondary atom (solute atom) to the grain boundary. The secondary atom(s) preferentially bond to the grain boundary because of the lowering of the energy at the grain boundary. The choice of solute atom is thus governed by the Grain Boundary Segregation energy, which is the lowering of the system energy due to reduction of the elastic misfit strain energy and the electronic (valence) interaction energy. The choice of secondary atoms can be aided by the use of DFT computations, as well as electronegativity and atomic elastic strain field energy calculations.

Faster secondary atoms may lead to better pinning of the grain boundary. It is also understood that a combination of more than one secondary atom may lead to better pinning of the grain boundary due to efficient boundary interstitial site filling (space-fill efficiency) due to the combination of varying secondary atom atomic radii. This is analogous to achieving better space filling when a mixture of different sized balls is used rather than a single sized ball.

A possible advantage of utilizing the solute drag method of grain boundary stabilization is that very low concentrations of secondary atoms, compared to solid solution strengthening or precipitation hardening, is needed. This in turn minimizes the impact of the modification on the plasmonic properties. Larger grain sizes possess smaller grain boundary area, and therefore require lower amounts of solute phase to percolate the boundary. In fact, only several hundred ppm of secondary atom (dopant) concentration may produce a 3 to 4 order of magnitude change in the grain boundary mobility. Initially the grain boundaries are pinned to the secondary atom atmospheres thereby immobilizing them. As the temperature is raised, the secondary atoms gain vibrational energy. The boundary then has an increasing tendency to decouple from the solute atoms pinning it. At a certain temperature, the boundary breaks away from the secondary atoms surrounding it. The breakaway temperature of the grain boundary is related to the concentration of secondary atoms at the boundary. Higher secondary atom concentrations at the boundary lead to higher break away temperatures. The NFT operating temperature will thus be dependent on the secondary atom concentration as shown schematically in FIG. 6.

FIG. 7 shows the solute segregation enthalpy of various atoms and indicates that atoms such as boron (B), and carbon (C); scandium (Sc); thallium (Th); and combinations thereof may be useful. Such atoms may have a higher propensity to grain boundary segregation and solute drag stabilization. As a general rule, elements with misfit energies (grain boundary solute segregation energies) higher than 12.5 kJ/mol will tend to easily segregate to the grain boundary. Therefore all the elements with segregation energies above the dashed lines can be considered candidates for alloying elements for solute drag strengthening of the Au NFT. Such elements can include, for example sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), antimony (Sb), thallium (Tl), boron (B), scandium (Sc), carbon (C), beryllium (Be), lutetium (Lu), thulium (Tm), erbium (Er), holmium (Ho), dysprosium (Dy), ytterbium (Yb), terbium (Tb), gadolinium (Gd), samarium (Sm), phosphorus (P), sulfur (S), promethium (Pm), neodymium (Nd), nickel (Ni), cobalt (Co), cerium (Ce), lanthanum (La), praseodymium (Pr), iron (Fe), and copper (Cu) for example. Elements included in FIG. 7 that have misfit energies less than 12.5 kJ/mol include europium (Eu), germanium (Ge), hafnium (Hf), cadmium (Cd), manganese (Mn), silicon (Si), barium (Ba), potassium (K), and rubidium (Rb).

In some embodiments, the amount of the secondary atom can be not less than 10 ppm (0.001 at %), or in some embodiments not less than 100 ppm (0.01 at %). In some embodiments, the amount of the secondary atom can be not greater than 100 pm (0.01 at %), in some embodiments not greater than 5 at %, or in some embodiments not greater than 10 at %.

In some embodiments, solute drag stabilization (or solute pinning) can be accomplished by carrying out the following steps prior to operating the NFT: (1) incorporation of one or more secondary atoms to the primary atom lattice; and (2) driving of the secondary atoms from the grain interior to the grain boundary through a suitably chosen temperature-time schedule. In some embodiments, secondary atoms that are added based on the solute drag mechanistic approach can be introduced through implantation, vacuum deposition, carburizing, nitridization, electrodeposition, incorporation through seed layers, or other techniques for example. Alternatively, secondary atom(s) may be introduced into the NFT by a variety of other methods. For example, the secondary atom(s) could be incorporated in the target material compositions which are deposited or co-deposited. Alternatively, secondary atom(s) could be incorporated into the NFT by ion implantation, by diffusion from or through the seed layer underneath.

Annealing can also optionally be included. The annealing schedule can be chosen so as to initially drive the secondary atoms from the grain interior to the grain boundary. The annealing temperature may help in the preferential segregation of the secondary atoms to the grain boundaries. Therefore, exposure of the NFT to heat during the annealing and operating temperature strengthens, rather than weakens the NFT alloy.

The method can be applicable to wafer and slider processing. Secondary atoms can be introduced at wafer (or slider) level for NFTs. The addition of secondary atom(s) can be advantageously combined with annealing to further improve NFT strength.

A particular illustrative example of a process sequence for implementation of the solute drag stabilization can include the following: deposit a gold film of the required thickness on a wafer (or slider bar); implant a carefully chosen species which lowers the total system energy at the grain boundary; for example, metals, metalloids, B, C, N, (O) at concentrations from about 100 ppm to 100000 ppm; implant conditions (temperature, voltage, dose, current) can be chosen and calculated so as to confine the implanted species (solute) in the thickness of the film; the wafer can be heated or cooled during the duration of the implant; the implant can be a line beam implanter, or it can be a Plasma immersion implanter, the implant can be a line of sight, or it can be in a retrograde profile; the implanted species can be implanted by itself, or it can be preceded or followed up by another co-implanted species which serves to control the degree of crystallinity, the dopant profile before and after the implant, the co implant can be a substitutional or an interstitial species, in some embodiments a substitutional species; a thermal activation anneal can then drive implant species to grain boundary from the grain interior, the time-temperature schedule can be carefully chosen; and the dose of the implant is chosen such that the penalty in n and k should be minimal.

The implementation of the solute dopant step can be preceded or followed by appropriate laser, furnace, spike or RTA processes. The aim of such processes are to advantageously modify and control the grain structure, point, line and volume defects of the gold for optimal reliability performance. These include vacancies, clusters, grain size, degree of crystallinity or amorphousness, twin and stacking fault density, grain boundary intergranular phases, etc. The annealing can be solid state annealing or epitaxy, or it can be liquid phase annealing or epitaxy.

It should be understood that the implantation and annealing steps can be carried out at sheet film of a plasmonic metal or a suitably chosen binary or ternary plasmonic alloy at wafer or bar level. It can also be combined with wafer or slider based patterning methods which can serve to selectively dope the solute atoms in only the needed regions of the wafer (slider) while protecting the other regions. Implementing such a process at the bar level may reduce the risk of damage to the optical layers of the NFT device from the implanted beam. An added benefit of such an implantation scheme is that there is no degradation in mechanical strength due to implant. Possible interfacial strength enhancements due to intentional mixing at interface are also possible.

Alternate methods of doping interstitials and solute atoms are also possible. For example, e-beam heating of the NFT film will lead to incorporation of carbon atoms. Likewise, the deposition of a metal layer (or carbon or boron) followed by a diffusion anneal, surface nitridation, surface carburization are also methods of incorporation of the secondary atom in the lattice. Alternatively, the dopant atom can be incorporated in the seed layer and driven by diffusion into the NFT material.

In some embodiments, disclosed NFTs may include a primary atom and at least one secondary atom, regardless of the mechanistic approach which is being relied upon as providing an effect. In some embodiments, a primary atom can be gold (Au) and the at least one secondary atom can be selected from: boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), hafnium (Hf), niobium (Nb), manganese (Mn), antimony (Sb), tellurium (Te), carbon (C), nitrogen (N), and oxygen (O), for example. In some embodiments, gold and B, Si or S can be utilized in a NFT. NFTs including gold and B, Si, S, or combinations thereof may be useful. In some embodiments, gold and In can be utilized in a NFT. NFTs including gold and In may be useful. In some embodiments, gold and B, C, N, or O can be utilized in a NFT. NFTs including gold and B, C, N, or O, or combinations thereof may be useful.

In some embodiments, disclosed NFTs may include gold (Au) and at least one of the following elements: erbium (Er), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), zinc (Zn). In some embodiments, disclosed NFTs may include gold (Au) and at least one of the following elements: barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), gadolinium (Gd), germanium (Ge), hydrogen (H), iodine (I), osmium (Os), phosphorus (P), rubidium (Rb), rhenium (Re), selenium (Se), samarium (Sm), terbium (Tb), thallium (Th).

Generally, a NFT can include a primary atom and at least one secondary atom. In some embodiments, the secondary atom(s) can have an atomic percent (at %) that is not greater than 50 at %, in some embodiments, not greater than 30 at %, in some embodiments, not greater than 5 at %, and in some embodiments, not greater than 1 at %. In some embodiments, the second atom(s) can have an at % that is not less than 0.001 at %, in some embodiments not less than 0.01 at %, and in some embodiments not less than 0.1 at %.

Disclosed NFTs may be made of a primary atom and at least one secondary atom. In some embodiments, the primary atom may have a higher atomic percentage (at %) in the NFT. In some embodiments, the primary atom may be silver (Ag), copper (Cu), or aluminum (Al). In some embodiments, more than one secondary atom is included in a NFT. A secondary atom(s) may be chosen by considering one or more properties of a material, mechanisms of atomic diffusion, or combinations thereof. Illustrative properties that can be considered can include enthalpy of mixing between the alloying element and the matrix element, enthalpy of segregation between the alloying element and the matrix element, plastic deformation, grain growth, and stress relaxation and creep, for example. Some of these properties have also been identified as the cause of various NFT failures.

In some embodiments, materials formed from a primary element and at least one secondary element can show relatively high resistance to grain growth, relatively high resistance to stress relaxation, enhanced hardness, high thermal conductivity, improved corrosion resistance, or some combination thereof.

In some embodiments, useful NFT materials can have optical properties that enable efficient coupling of incident light to the surface plasmons and effective energy transfer to the magnetic medium. The optical properties of NFT materials are often characterized by their optical refractive index (n) and extinction coefficient (k) which can be measured by ellipsometry. From the n and k values, the real and imaginary part of the dielectric constant (permittivity) can be calculated by: ∈₁=n²−k² and ∈₂=2nk. The plasmonic effect arises from the negative real part of the dielectric constant of the material. The strength of plasmonic coupling depends on the absolute value of ∈₁. On the other hand, the surface plasmon mode needs to propagate over a substantial distance. The loss of this propagation is proportional to the imaginary part of the dielectric ∈₂. A good plasmonic material will have high |∈₁| and low ∈₂. Hence a figure-of-merit (FOM) has been developed to characterize the “goodness” of plasmonic materials: FOM=3*|∈₁/∈₂|.

The property of grain growth can be relevant to the ability of an alloy to function in a NFT. One of the sources for silver, copper, or aluminum deformation is significant grain growth at high temperatures. By alloying with other soluble metal atoms, the grain size of the alloy can be reduced and the grain growth can be impeded. The segregation of a second element to the grain boundaries of a metal can provide stabilization at the nanocrystalline level. In addition to slowing the migration kinetics of grain boundaries, segregated atoms can perform a primary stabilization function by lowering the energy associated with the grain boundary. This lowering of the grain boundary energy occurs numerically as a function of the enthalpy of grain boundary segregation and the amount of excess solute at the grain boundaries.

For the case of nanocrystalline stabilization, segregating alloying additions are specifically desirable. In order to identify which elements are best suited for segregation in stabilization in nanocrystalline environments, the enthalpy of mixing and the enthalpy of grain boundary segregation should both be positive, with an enthalpy of segregation higher than 20 kJ/mol and a ratio of Hseg/Hmix≧1. If the alloying elements are chosen correctly to coincide with this, the inherent driving force for this grain growth can actually be removed entirely. It is thought, but not relied upon that impeding grain growth can be the result of: a larger area of grain boundary that restrains the dislocation movement; and the localized strain fields by impurities that hinder the dislocation motion.

Enthalpies of mixing and of grain boundary segregation assuming a silver matrix, a copper matrix, and an aluminum matrix have been calculated. From these calculations, particular secondary elements have been identified that may provide stabilizing effects to a nanocrystalline state. The calculations for the primary element being silver are shown in FIG. 8, the primary element being copper are shown in FIG. 10 and the primary element being aluminum are shown in FIG. 11.

FIG. 8 affords selection of secondary elements for instances in which the primary element is silver (Ag). In some embodiments, a NFT can include silver (Ag) as a primary element and at least one secondary element selected from: sodium (Na), thallium (Tl), bismuth (Bi), lead (Pb), potassium (K), cesium (Cs), rubidium (Rb), beryllium (Be), boron (B), manganese (Mn), or combinations thereof for example. In some embodiments, a NFT can include silver (Ag) as a primary element and at least one secondary element selected from: boron (B), beryllium (Be), bismuth (Bi), and cesium (Cs), or combinations thereof for example.

In some embodiments, secondary atom(s) can also be chosen based on other considerations. For example, secondary atom(s) can be chosen based on mechanistic considerations involved in pinning grain growth. The NFT grain and interface boundary can be atomically engineered by the preferential adsorption of secondary atom(s) in order to pin the grain boundary and improve the grain boundary migration resistance of a NFT that includes, a primary atoms, such as gold for example. This can also be described as utilizing minor alloying elements (e.g., secondary atom(s)) to alter the fundamental grain boundary migration kinetics of the primary atom (e.g., gold). Mechanical high temperature reliability of the NFT may therefore be improved by intentional microalloying additions of one or more secondary atom(s) into the NFT material. Such intentional alloying can pin the grain boundary movement by the so called “solute drag” effect, making it harder for the peg to recess.

Disclosed concepts may provide stable NFT element dimensions during operating temperatures by pinning grain growth. This concept utilizes the preferential placement of secondary atoms at the grain boundaries of the NFT material to pin grain movement. The secondary atoms are chosen such that the total strain energy and total chemical potential energy of the system of atoms is reduced when they are at the grain boundary. Thus the grain boundary secondary atom is in a potential “well” and therefore “locks” the movement of the grain boundary.

The preferential placement of secondary atoms can be accomplished by facilitating the movement of secondary atoms to the grain boundaries. Such secondary atoms may be able to stabilize the NFT against grain growth through the following mechanisms: increased drag force on the moving grain boundary due to the binding chemical potential and elastic strain interaction of secondary atom to the grain boundary; reduction of grain boundary diffusion by poisoning of the primary atom (e.g., gold) grain boundary by the tightly adsorbed secondary atoms blocking of the diffusion jump sites at the boundary by the secondary atoms; reduction of the efficiency of secondary atom transfer across the grain boundary by the secondary atom; change in the grain boundary structure brought about by the secondary atom; preferential formation of vacancy-secondary atom pairs and secondary atom-primary atom pairs at the grain boundary which make boundary migration harder; improving the grain boundary cohesion; or some combination thereof.

The selection of the secondary atom can be based, at least in part on considerations involving the energetics of segregation of the secondary atom to the grain boundary. One consideration is the size of the secondary atom. In some embodiments the size of the secondary atom can be less than the size of the primary atom. If such a relationship exists the secondary atom can occupy interstitial positions in the bulk and at the grain boundary. In a face centered cubic (FCC) structure, the octahedral site is the largest interstitial site. The same basic mechanism allows the secondary atom to poison the grain boundary/surface diffusivity. Secondary atoms having smaller radii may be more amenable to providing this effect. Grain boundary precipitants may also be formed based on the energetics of the system.

It should be understood, having read this disclosure, that grain boundaries as discussed herein include high angle and low angle grain boundaries, coherent and incoherent boundaries, tilt and twist boundaries, intergranular phases as well as high symmetry boundaries such as twin boundaries.

An important consequence of these considerations is that NFTs without secondary atom(s) will have higher grain boundary mobilities and lower stabilities. Thus NFTs as typically formulated will have lower resistance to grain boundary movement since, by definition, they do not have secondary atoms in the system that can preferentially locate to the grain boundary. They will therefore possess undesirable grain migration and reliability performance.

In contrast, disclosed NFTs can utilize a secondary atom(s) to pin the grain boundary. A secondary atom(s) present even at a few 10s or 100s of ppm may make a dramatic impact in curtailing the mobility of the grain boundaries. Secondary atom(s) which reduce the strain energy and chemical potential at the grain boundary may lead to preferential clustering of secondary atoms near the grain boundaries (called Cottrell atmospheres) which may provide locking mechanisms that impede grain boundary movement. It should be emphasized that the primary function of the secondary atom(s) is grain boundary mobility impairment, although other functions such as solid solution strengthening are also possible.

A secondary atom can be chosen based, at least in part, on the ability for preferential segregation of the secondary atom (solute atom) to the grain boundary. The secondary atom(s) preferentially bond to the grain boundary because of the lowering of the energy at the grain boundary. The choice of solute atom is thus governed by the Grain Boundary Segregation energy, which is the lowering of the system energy due to reduction of the elastic misfit strain energy and the electronic (valence) interaction energy. The choice of secondary atoms can be aided by the use of DFT computations, as well as electronegativity and atomic elastic strain field energy calculations.

Faster secondary atoms may lead to better pinning of the grain boundary. It is also understood that a combination of more than one secondary atom may lead to better pinning of the grain boundary due to efficient boundary interstitial site filling (space-fill efficiency) due to the combination of varying secondary atom atomic radii. This is analogous to achieving better space filling when a mixture of different sized balls is used rather than a single sized ball.

A possible advantage of utilizing the solute drag method of grain boundary stabilization is that very low concentrations of secondary atoms, compared to solid solution strengthening or precipitation hardening, is needed. This in turn minimizes the impact of the modification on the plasmonic properties. Larger grain sizes possess smaller grain boundary area, and therefore require lower amounts of solute phase to percolate the boundary. In fact, only several hundred ppm of secondary atom (dopant) concentration may produce a 3 to 4 order of magnitude change in the grain boundary mobility. Initially the grain boundaries are pinned to the secondary atom atmospheres thereby immobilizing them. As the temperature is raised, the secondary atoms gain vibrational energy. The boundary then has an increasing tendency to decouple from the solute atoms pinning it. At a certain temperature, the boundary breaks away from the secondary atoms surrounding it. The breakaway temperature of the grain boundary is related to the concentration of secondary atoms at the boundary. Higher secondary atom concentrations at the boundary lead to higher break away temperatures.

FIG. 9A show the solute segregation enthalpy of various atoms. Useful atoms may have a higher propensity to grain boundary segregation and solute drag stabilization. As a general rule, elements with misfit energies (grain boundary solute segregation energies) higher than 12.5 kJ/mol may tend to easily segregate to the grain boundary. Therefore all the elements with segregation energies above the dashed lines can be considered candidates for alloying elements for solute drag strengthening of the Ag NFT.

In some embodiments a NFT can include silver (Ag) as the primary element and at least one secondary element selected from: sodium (Na), strontium (Sr), calcium (Ca), boron (B), scandium (Sc), carbon (C), beryllium (Be), yttrium (Y), thorium (Th), antimony (Sb), lead (Pb), tin (Sn), thallium (Tl), lutetium (Lu), thulium (Tm), erbium (Er), holmium (Ho), ytterbium (Yb), gadolinium (Gd), samarium (Sm), promethium (Pm), praseodymium (Pr), sulfur (S), neodymium (Nd), phosphorus (P), cerium (Ce), lanthanum (La), iron (Fe), nitrogen (N), oxygen (O), molybdenum (Mo), and combinations thereof. In some embodiments a NFT can include silver (Ag) as the primary element and at least one secondary element selected from: calcium (Ca), boron (B), carbon (C), boron (B), yttrium (Y), thorium (Th), antimony (Sb), tin (Sn), nitrogen (N), or some combination thereof, for example In some embodiments a NFT can include silver (Ag) as the primary element and at least one secondary element selected from: cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), magnesium (Mg), or combinations thereof for example.

Silver can be prone to tarnish. Therefore, the addition of a secondary element(s) can also improve the corrosion resistance of the silver. Such secondary elements may generally have low solute segregation energies below 15 kJ/mol as shown in FIG. 9A (FIGS. 9B and 9C are the same graph as FIG. 9A but have expanded scales at the lower end of the segregation enthalpy). Illustrative secondary element(s) that may also improve corrosion resistance can include, for example chromium (Cr), nickel (Ni), tantalum (Ta), rubidium (Rb), ruthenium (Ru), vanadium (V), gold (Au), palladium (Pd), platinum (Pt), aluminum (Al), or some combination thereof can be utilized as a secondary element. In some embodiments any element added to silver may improve the corrosion and tarnish resistance. In some embodiments, the atomic size difference between the silver (solvent) atom and the secondary atom (solute atom) should be no more than 15% and the electronegativity of the secondary atom should be within +/−0.5 units of the electronegativity of silver. In some embodiments, illustrative secondary element(s) can include carbon (C), boron (B), nitrogen (N), or combinations thereof for example.

FIG. 10 affords selection of secondary elements for instances in which the primary element is copper (Cu). In some embodiments, a NFT can include copper (Cu) as a primary element and at least one secondary element selected from: cadmium (Cd), mercury (Hg), indium (In), antimony (Sb), sodium (Na), thallium (Tl), potassium (K), cesium (Cs), rubidium (Rb), bismuth (Bi), lead (Pb), tin (Sn), or combinations thereof for example. In some embodiments, a NFT can include copper (Cu) as a primary element and at least silver (Ag) as a secondary element.

FIG. 11 affords selection of secondary elements for instances in which the primary element is aluminum (Al). In some embodiments, a NFT can include aluminum (Al) as a primary element and at least one secondary element selected from: boron (B), beryllium (Be), antimony (Sb), tin (Sn), mercury (Hg), indium (In), lead (Pb), bismuth (Bi), thallium (Tl), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or combinations thereof for example

Generally, a NFT can include a primary atom and at least one secondary atom. In some embodiments, the secondary element(s) can have an atomic percent (at %) that is not greater than 15 at %, and in some embodiments, not greater than 5 at %. In some embodiments, the secondary element(s) can have an at % that is not less than 0.01 at %, or in some embodiments not less than 0.1 at %.

Disclosed herein are methods of forming NFTs that include a primary element and at least one secondary element. Primary elements may include, gold (Au), silver (Ag), copper (Cu), aluminum (Al), or combinations thereof, for example. In some embodiments, the secondary atom can include those disclosed in U.S. Pat. No. 8,427,925, U.S. Patent Publication Number 20140050057, U.S. patent application Ser. No. 13/923,925 entitled MAGNETIC DEVICES INCLUDING FILM STRUCTURES, U.S. patent application filed on the same day herewith having Ser. No. 14/313,651 entitled MATERIALS FOR NEAR FIELD TRANSDUCERS AND NEAR FIELD TRANSDUCERS CONTAINING SAME, U.S. patent application filed on the same day herewith having Ser. No. 14/313,528 entitled MATERIALS FOR NEAR FIELD TRANSDUCERS AND NEAR FIELD TRANSDUCERS CONTAINING SAME, and U.S. patent application filed on the same day herewith having Ser. No. 14/313,717 entitled MATERIALS FOR NEAR FIELD TRANSDUCERS AND NEAR FIELD TRANSDUCERS CONTAINING SAME, the entire disclosures of which are all incorporated herein by reference thereto.

In some embodiments, the at least one secondary atom can be boron (B), bismuth (Bi), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), cesium (Cs), carbon (C), antimony (Sb), gadolinium (Gd), samarium (Sm), thallium (Tl), hafnium (Hf), niobium (Nb), manganese (Mn), erbium (Er), zinc (Zn), nitrogen (N), oxygen (O), osmium (Os), phosphorus (P), rhenium (Re), beryllium (Be), yttrium (Y), sodium (Na), strontium (Sr), thulium (Tm), promethium (Pm), lanthanum (La), cerium (Ce), cobalt (Co), nickel (Ni), neodymium (Nd), ytterbium (Yb), lead (Pb), magnesium (Mg), calcium (Ca), iron (Fe), molybdenum (Mo), zirconium (Zr), chromium (Cr), gallium (Ga), potassium (K), lithium (Li), rhodium (Rh), vanadium (V), titanium (Ti), tantalum (Ta), platinum (Pt), thorium (Th), cadmium (Cd), palladium (Pd), technetium (Tc), ruthenium (Ru), tungsten (W), mercury (Hg), or combinations thereof for example. In some embodiments a secondary atom can include silver (Ag), copper (Cu), aluminum (Al), or gold (Au) in combination with a primary atom that is not the same, e.g., a NFT could include gold as the primary atom and silver as the secondary atom, but a NFT could not include gold as the primary atom and gold as the secondary atom. One or more than one secondary atom can be utilized. Useful amounts of secondary elements can be introduced into a primary element film with relatively modest penalties to the plasmonic properties, optical properties, thermal properties, or combinations thereof.

In some embodiments, a primary element can include silver (Ag), copper (Cu), or aluminum (Al). In some embodiments where the primary element is silver (Ag) at least one secondary element can be selected from: sodium (Na), thallium (Tl), bismuth (Bi), lead (Pb), potassium (K), cesium (Cs), rubidium (Rb), beryllium (Be), boron (B), manganese (Mn), or combinations thereof for example. In some embodiments where the primary element is silver (Ag) at least one secondary element can be selected from: sodium (Na), strontium (Sr), calcium (Ca), boron (B), scandium (Sc), carbon (C), beryllium (Be), yttrium (Y), thorium (Th), antimony (Sb), lead (Pb), tin (Sn), thallium (Tl), lutetium (Lu), thulium (Tm), erbium (Er), holmium (Ho), ytterbium (Yb), gadolinium (Gd), samarium (Sm), promethium (Pm), praseodymium (Pr), sulfur (S), neodymium (Nd), phosphorus (P), cerium (Ce), lanthanum (La), iron (Fe), nitrogen (N), oxygen (O), molybdenum (Mo), and combinations thereof. In some embodiments where the primary element is silver (Ag) at least one secondary element can be selected from: cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), magnesium (Mg), or combinations thereof for example. In some embodiments where the primary element is silver (Ag) at least one secondary element can be selected from: gold (Au), palladium (Pd), platinum (Pt), aluminum (Al), or some combination thereof. In some embodiments where the primary element is copper (Cu) at least one secondary element can be selected from: cadmium (Cd), mercury (Hg), indium (In), antimony (Sb), sodium (Na), thallium (Tl), potassium (K), cesium (Cs), rubidium (Rb), bismuth (Bi), lead (Pb), tin (Sn), or combinations thereof. In some embodiments where the primary element is copper (Cu) at least silver (Ag) can be included as a secondary element. In some embodiments where the primary element is aluminum (Al) at least one secondary element can be selected from: boron (B), beryllium (Be), antimony (Sb), tin (Sn), mercury (Hg), indium (In), lead (Pb), bismuth (Bi), thallium (Tl), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or combinations thereof.

Disclosed herein are numerous methods of forming a NFT having a primary element and at least one secondary element. Generally, the various types of methods disclosed herein include depositing or co-depositing the primary and secondary element(s) from a target(s); incorporating the secondary element(s) into the NFT by diffusion from a seed layer; utilizing surface carburization, boronization, or nitridation; by ion implantation; or combinations thereof.

Deposition

Disclosed methods can utilize deposition from a target material. Deposition can be accomplished using a target that includes both the primary and secondary element or it can be accomplished using separate targets, one of which includes the primary element and the other including the secondary element. An annealing step can be undertaken after the primary and secondary elements are deposited. The annealing step can be designed to drive the secondary element from the interior of the grain to the grain boundary. The annealing step providing better properties to the NFT material can be advantageous because the entire device may require an annealing step. Annealing conditions, such as temperature and time would be known to one of skill in the art, having read this specification.

Diffusion from Seed Layer

A NFT that includes a primary element and at least one secondary element may also be formed by forming a seed layer that includes the secondary element(s) and then driving some of that material into the already deposited primary element material. Diffusion of some of the secondary element from the seed layer to the primary element in the NFT (or NFT precursor) can be accomplished through annealing. Annealing conditions, such as temperature and time would be known to one of skill in the art, having read this specification.

Carburizing/Boronizing/Nitriding

A NFT that includes a primary element and at least one secondary element may also be formed by exposing a NFT (or NFT precursor) made of the primary element to heat treatment in an atmosphere that contains the secondary element. Such processes can be utilized by, for example vaporizing the secondary element in the presence of the NFT (or NFT precursor) in an elevated temperature environment. Such processes can also be referred to, in some instances as carburizing (where carbon is the secondary element), nitriding (where nitrogen is the secondary element), boronizing or boriding (where boron is the secondary element), or carbonitriding (where both carbon and nitrogen are the secondary elements) for example.

Ion Implantation

One of the potential issues with conventional sputtering techniques when sputtering alloy films (including a primary element and at least one secondary element) is the possibility of the secondary element(s) segregating and separating to the grain boundary during the deposition process. The problem can be exacerbated at lower film thicknesses or low dopant or alloying element concentrations, where the secondary element could diffuse out to the surface of the film. Lighter secondary elements have higher mobility and are therefore prone to higher diffusion. This could result in deviations of the composition of the NFT from a targeted composition. Formation of a NFT (or precursor) using ion implantation can alleviate such problems.

In some embodiments specific ion implantation methods that can be utilized can include beam line implants, or plasma immersion implants for example. The ion beam used for implanting secondary element(s) can be from a beam line producing a pure or skewed Gaussian profile, or a plasma ion immersion system forming an error function dopant profile. Implantation of the secondary element(s) can be carried out at elevated temperature or at cryogenic or cold temperature.

Any of the disclosed methods can be carried out on planar surfaces, on sloped or contoured surfaces, on surfaces with retrograde wall angles, or any combination thereof. Although formation of NFT elements are specifically contemplated and discussed herein, it will be understood by one of skill in the art that disclosed methods can also be utilized in the formation of heat sink elements, for example, as well.

In some embodiments, the secondary element could have a substantially constant concentration across the NFT (or NFT precursor) or could have a concentration that changes. The profile of the secondary element(s), which can also be referred to as the dopant in the context of an ion implantation process through the thickness of the film could be Gaussian, or could be an error function dopant distribution for example. In some embodiments, the secondary element could be implanted at the same energy throughout the primary element or could be implanted at different energies at different portions of the film. The energy of implantation can control, at least in part, the depth at which the secondary element is implanted in the film of the primary element. The energy for the implantation could be a single energy, or it could be a combination of energies for example. In embodiments where more than one energy is utilized, the profiles of each could additively be used to shape and tailor the final profile (e.g., the depth profile) of the secondary element in the film.

In addition to through thickness tailoring of the composition profile, the composition could alternatively (or in combination) be spatially varied across the breadth or expanse of the film (e.g., the wafer diameter). For example, the center of the wafer could have a first composition profile while the edge of the wafer could have a second and different composition profile. In some embodiments more than one secondary element could be implanted in a primary element film, each optionally having a chosen through thickness and across wafer composition profile. The sequence in which the secondary elements are implanted can be chosen such that the diffusivity and the crystallinity of the film can be advantageously affected.

The concentration of the secondary element can be varied from several 10s of ppm to several atomic percent. In some embodiments, the secondary element can have a concentration that is not less than 10 ppm (or 0.001 atomic percent, at %), or in some embodiments not less than 100 ppm (0.01 at %). In some embodiments, the secondary element can have a concentration that is not greater than 10 at %, or in some embodiments not greater than 5 at %. The concentration of the secondary element can be controlled (e.g., metered in real time) using electrical methods, for example. Because control can be accomplished using electrical control, precise and repeatable control should be relatively easy to obtain.

In some embodiments, an optional post anneal thermal treatment could be used to further shape the dopant profile in the NFT. In some embodiments, another optional step can be carried out before the optional annealing step, e.g., a metal or dielectric cap layer can be deposited on the NFT film surface. In some embodiments, multiple thermal treatments, multiple implantation steps, or combinations thereof can be carried out.

NFTs produced using implantation methods can offer advantages (over co-deposition methods, for example) because secondary elements introduced via ion implantation generally remain in the lattice due to the physics of the implantation process. Specifically, implantation processes are not constrained by thermodynamic equilibrium or stoichiometry and therefore separation or segregation of the secondary element is not likely to occur.

Disclosed methods can also include another step after the implantation step, where the NFT layer (made up of the primary element film implanted with the at least one secondary element) is patterned into a NFT. The step of patterning can include one or more than one step and can utilize known patterning processes including, for example photolithography, etching, etc.

In some embodiments secondary elements may be incorporated into a primary element layer that is covered or at least partially encapsulated with a dielectric or metal layer. As described above, one of the potential concerns when incorporating dopants (e.g., secondary elements) at low levels in NFT films is grain boundary and surface segregation of the dopant atoms, especially lighter atoms as well as those with limited solubility in the primary element film lattice. Surface oxidation of the secondary element could also lead to depletion of the secondary element from the interior of the film. Thermal exposure of the NFT film after the alloying or film formation step could therefore lead to deviations in composition from a targeted composition.

To mitigate these effects, the implantation of the at least one secondary element into the primary element film can be carried out after a protective metal or dielectric layer is deposited on the primary element film. The protective metal or dielectric layer can be referred to as an encapsulate layer. The encapsulant layer seals off the surface of the primary element film from the exterior atmosphere thereby suppressing loss of the implanted secondary element to the atmosphere during and after processing. Use of an encapsulant layer can be especially advantageous when implanting in relatively thin films or with secondary elements that have mobility or segregation tendencies. Use of an oxide encapsulant layer may also help the film layer maintain planarity during subsequent thermal annealing steps by preventing or minimizing possible thermal grooving of the grain boundaries.

The encapsulant layer can include metals or dielectric materials. Illustrative dielectric materials can include dielectric oxides such as alumina, silica, yttria, zirconia, tantala, titania, niobia, or combinations thereof, for example. The encapsulant layer can also include a metal or an alloy of a metal. In some embodiments, a material for an encapsulant layer can be selected based on its compatibility with further processing that will be carried out on the article (e.g., wafer or rowbar processing). In some embodiments, the material can be a material that will be part of the larger device, or it should be one that can be removed (in some embodiments relatively easily removed) subsequent to implantation.

The encapsulant layer can have a thickness that is not less than 2 nm, or in some embodiments not less than 5 nm. In some embodiments, the encapsulant layer can have a thickness that is not greater than 100 nm, or in some embodiments not greater than 30 nm. In some embodiments, part of the encapsulant layer is consumed during the implantation process due to sputtering of the surface atoms. As such, the encapsulant layer thickness may be dynamically varied to intentionally shift the position of “Rp” and “delta Rp” (Rp is the statistical mean depth from the sample/film surface where the peak dopant concentration would occur; and delta Rp refers to the sigma or the spread of the dopant concentration profile across the thickness of the implanted film). The progressive shifting of the peak profile position ‘Rp” during the implant process can be advantageously used to control the dopant localization and mixing. Sometimes, while carrying out the implantation of an NFT or heat sink element through the encapsulant oxide, the constituent element of the oxide can also preferentially get knocked into the NFT or heat sink film during implant. The extent of this encapsulant film knock in in the underlying film can be controlled by controlling the encapsulant oxide thickness as well as the implanted dose.

In some embodiments, more than one secondary element can be implanted through the encapsulant layer, each with its own (same or different) implantation parameters. In some embodiments, the ion beam can be directed at a normal angle (90 degree) to the wafer or sample surface, or it can be incident at an angle ranging anywhere from 1 degree to 90 degrees, relative to the wafer or sample surface. In some embodiments, the sample can be stationary during the implantation, or it can be rotated at a fixed or variable rate of speed during implanting.

Implantation with or without an encapsulation layer can be carried out at various stages of processing and formation of NFTs (or other elements). In some embodiments secondary elements may be incorporated into a film or layer of the primary element through ion implantation before the film or layer is formed into a NFT, or at a stage where the air bearing surface (ABS) of the NFT (and surrounding device) is being defined. Regardless of the timing of when the implantation is being done, the implantation can be done globally into the surface or it can be carried out in conjunction with a mask that allows only selected areas of the surface to be implanted.

Ion implantation being undertaken during ABS definition can be done at various stages, including for example at rough lap, at final lap, after the first layer of head overcoat has been deposited, or after the entire layer of head overcoat has been deposited. In some embodiments, a Gaussian dopant profile can be implanted at rough lap, followed by a final lap, whose final thickness can be set to advantageously coincide with the ‘Rp” of the implanted Gaussian distribution. In some embodiments, the ABS surface can be subject to plasma immersion ion implantation, with the error function like distribution of the secondary element leading away from the ABS.

In some embodiments, more than one secondary element, each with its own energy and dose profile can be implanted into the ABS rowbar, for example. Such implantation could be carried out to improve the performance of the NFT element, to advantageously modify the properties of the head overcoat, or both. The implantation can also be done to advantageously modify the corrosion resistance of the write pole material. Implantation carried out after the deposition of a partial or full head overcoat may serve to “lock” the secondary element inside the active device structure (write pole or NFT), thereby serving to improve its efficacy.

Implantation at an ABS processing stage can also optionally be combined with sequential oxidation processes to form thin metal oxides for protection purposes.

The methods discussed above can be utilized to produce different types of implanted NFT layers (or NFTs). Illustrative examples of such can include interfacial mixing and localization of the implanted species at interfaces and graded interfaces, for example.

In some embodiments, secondary element(s) can be implanted so as to be preferentially located at the dielectric-metal interface. The dielectric-metal interfaces (e.g., dielectric-NFT interfaces and dielectric-heat sink interface) being referred to herein can include the core to NFT space/NFT interface (referred to herein as the CNS/NFT interface), the NFT to pole space/NFT interface (referred to herein as the NPS/NFT interface), or the NFT to pole space/heat sink interface (referred to herein as the NPS/Heat Sink interface). Preferential placement of the secondary element(s) within a few nanometers of such interfaces can lead to intentional mixing or rearrangement of the atoms at the interface due to primary atomic collisions as well as recoil collisions arising from the implanted atom. This may lead to advantageous interfacial stabilization.

It is thought, but not relied upon that if the secondary element(s) is not located within a few nanometers of the NFT/dielectric interface, the presence of excess dopant atoms in the NFT may diminish or even eliminate the plasmonic properties of the NFT material, or contribute to excessively high optical propagation losses in the dielectric material. Secondary element(s) chosen may be chosen so as to minimize the straggle or the lateral spread at the interface. Parameters such as the atomic weight, the incidence angle of implantation, the dose and the incident beam energy, or combinations thereof can be chosen so as to control the interfacial localization. Advantage can be taken of the steepness of the dopant profile gradient to place the interfacial mixing layer so as to minimize and control the dopant spread into the NFT layer to within a few nanometers. For the case of beam implants, the position of the “Rp” parameter and the “delta Rp” parameter can be carefully controlled so as to achieve the desired interfacial mixing.

In some embodiments, more than one secondary element(s) can be preferentially located at one or more interfaces. Subsequent to the implant step, the secondary elements can be appropriately activated so as to react with each other, or with the dielectric or metal layer, to form an intermediary layer that may aid in bonding of the dielectric layer to the metal NFT element.

The tilt angle used when implanting to impart interfacial mixing can depend, at least in part, on the device geometry (planar vs. contoured 3D structures, etc.) as well as other considerations. Larger tilt angles may lead to better mixing, but at the expense of larger secondary element path length through the encapsulant layer. Therefore a smaller fraction of the dopant would localize at the interface, leading to an overall decrease in the implant efficiency.

In some embodiments, implantation of a secondary element(s) may be utilized to form a graded interface or graded implantation. A graded implantation may be advantageous in controlling the film stresses, thermal stresses, CTE stresses, optical properties, or some combination thereof. One method of forming a graded implantation can include first depositing a primary element layer having a thickness that is less than the final desired thickness. In some embodiments, such a layer can have a thickness from 0.1 nm to 20 nm, and may be deposited on top of the CNS layer (for example). Next, the secondary element(s) can be implanted into the primary element layer. In such embodiments, the secondary element(s) can be one that may serve to advantageously improve the film densification, enhance the interfacial strength of the interface on which it is deposited, or a combination thereof (e.g., the CNS/NFT interface). Such a species may have mutual affinity for the NFT film and the dielectric material (e.g., the CNS material). An example of such a secondary element can include sulfur (S), which may preferentially bond to the gold. Such implantation processes and primary element layer deposition processes can be carried out alternatively in a repeated sequence, thereby forming a layered or a graded structure.

In some embodiments, more than one secondary element can be utilized. In such embodiments, the at least two secondary elements may react with each other, or one or more of them may react with the dielectric material surface, one or more of them may react with the primary element film during the growth process to improve the density and the interfacial strength, or some combination thereof. In a particular illustrative embodiment, gold deposition as the primary element layer may be combined with co-implantation of one or more secondary elements, followed by subsequent deposition and implantation sequences to form a relatively more dense and compacted NFT structure.

It should be understood, having read this specification, that the process of interface strengthening and initial film densification as described herein, while applicable to NFT materials such as Au, Ag, Al, Cu, etc., are also equally applicable to the formation of interconnect processes in semiconductor manufacturing. It should also be understood that such modifications can be used advantageously in the manufacture of trench liners, via liners, etc. that can be subsequently used for write pole processing, damascene copper processes, etc. Use of such methods may lead to advantageous gains in electromigration resistance, reliability, or other such properties for example.

Methods disclosed herein may form NFTs that offer advantageous properties based on various mechanistic reasoning. The NFT grain and interface boundary can be atomically engineered by the preferential adsorption of secondary atom(s) in order to pin the grain boundary and improve the grain boundary migration resistance of a NFT that includes, a primary atoms, such as gold for example. This can also be described as utilizing minor alloying elements (e.g., secondary atom(s)) to alter the fundamental grain boundary migration kinetics of the primary atom (e.g., gold). Mechanical high temperature reliability of the NFT may therefore be improved by intentional microalloying additions of one or more secondary atom(s) into the NFT material. Such intentional alloying can pin the grain boundary movement by the so called “solute drag” effect, making it harder for the peg to recess.

Disclosed concepts may provide stable NFT element dimensions during operating temperatures by pinning grain growth. This concept utilizes the preferential placement of secondary atoms at the grain boundaries of the NFT material to pin grain movement. The secondary atoms are chosen such that the total strain energy and total chemical potential energy of the system of atoms is reduced when they are at the grain boundary. Thus the grain boundary secondary atom is in a potential “well” and therefore “locks” the movement of the grain boundary.

The preferential placement of secondary atoms can be accomplished by facilitating the movement of secondary atoms to the grain boundaries. Such secondary atoms may be able to stabilize the NFT against grain growth through the following mechanisms: increased drag force on the moving grain boundary due to the binding chemical potential and elastic strain interaction of secondary atom to the grain boundary; reduction of grain boundary diffusion by poisoning of the primary atom (e.g., gold) grain boundary by the tightly adsorbed secondary atoms blocking of the diffusion jump sites at the boundary by the secondary atoms; reduction of the efficiency of secondary atom transfer across the grain boundary by the secondary atom; change in the grain boundary structure brought about by the secondary atom; preferential formation of vacancy-secondary atom pairs and secondary atom-primary atom pairs at the grain boundary which make boundary migration harder; improving the grain boundary cohesion; or some combination thereof.

It should be understood, having read this disclosure, that grain boundaries as discussed herein include high angle and low angle grain boundaries, coherent and incoherent boundaries, tilt and twist boundaries, intergranular phases as well as high symmetry boundaries such as twin boundaries.

An important consequence of these considerations is that NFTs without secondary atom(s) will have higher grain boundary mobilities and lower stabilities. Thus NFTs as typically formulated will have lower resistance to grain boundary movement since, by definition, they do not have secondary atoms in the system that can preferentially locate to the grain boundary. They will therefore possess undesirable grain migration and reliability performance.

In contrast, disclosed NFTs can utilize a secondary atom(s) to pin the grain boundary. A secondary atom(s) present even at a few 10s or 100s of ppm may make a dramatic impact in curtailing the mobility of the grain boundaries. Secondary atom(s) which reduce the strain energy and chemical potential at the grain boundary may lead to preferential clustering of secondary atoms near the grain boundaries (called Cottrell atmospheres) which may provide locking mechanisms that impede grain boundary movement. It should be emphasized that the primary function of the secondary atom(s) is grain boundary mobility impairment, although other functions such as solid solution strengthening are also possible.

A secondary atom can be chosen based, at least in part, on the ability for preferential segregation of the secondary atom (solute atom) to the grain boundary. The secondary atom(s) preferentially bond to the grain boundary because of the lowering of the energy at the grain boundary. The choice of solute atom is thus governed by the Grain Boundary Segregation energy, which is the lowering of the system energy due to reduction of the elastic misfit strain energy and the electronic (valence) interaction energy. The choice of secondary atoms can be aided by the use of DFT computations, as well as electronegativity and atomic elastic strain field energy calculations.

Faster secondary atoms may lead to better pinning of the grain boundary. It is also understood that a combination of more than one secondary atom may lead to better pinning of the grain boundary due to efficient boundary interstitial site filling (space-fill efficiency) due to the combination of varying secondary atom atomic radii. This is analogous to achieving better space filling when a mixture of different sized balls is used rather than a single sized ball.

A possible advantage of utilizing the solute drag method of grain boundary stabilization is that very low concentrations of secondary atoms, compared to solid solution strengthening or precipitation hardening, is needed. This in turn minimizes the impact of the modification on the plasmonic properties. Larger grain sizes possess smaller grain boundary area, and therefore require lower amounts of solute phase to percolate the boundary. In fact, only several hundred ppm of secondary atom (dopant) concentration may produce a 3 to 4 order of magnitude change in the grain boundary mobility. Initially the grain boundaries are pinned to the secondary atom atmospheres thereby immobilizing them. As the temperature is raised, the secondary atoms gain vibrational energy. The boundary then has an increasing tendency to decouple from the solute atoms pinning it. At a certain temperature, the boundary breaks away from the secondary atoms surrounding it. The breakaway temperature of the grain boundary is related to the concentration of secondary atoms at the boundary. Higher secondary atom concentrations at the boundary lead to higher break away temperatures.

In some embodiments disclosed NFTs can be made using alternate methods of doping interstitial atoms or solute atoms. In some embodiments electron beam heating of a NFT film can lead to carbon incorporation. In some embodiments the deposition of a metal layer (or carbon or boron for example) followed by a diffusion anneal can be utilized. In some embodiments, surface nitridization or surface carburization of a deposited NFT film can be utilized to incorporate nitrogen or carbon. In some embodiments, a dopant atom(s) can be incorporated into the seed layer and then driven by diffusion into the NFT material.

In some embodiments, a secondary atom or more than one secondary atom can be chosen from: sodium (Na), nickel (Ni), silicon (Si), vanadium (V), yttrium (Y), nitrogen (N), oxygen (O), lanthanum (La), neodymium (Nd), strontium (Sr), platinum (Pt), beryllium (Be), calcium (Ca), cerium (Ce), gallium (Ga), potassium (K), lithium (Li), germanium (Ge), cadmium (Cd), cobalt (Co), erbium (Er), iridium (Ir), molybdenum (Mo), phosphorus (P), lead (Pb), promethium (Pm), rhenium (Re), rhodium (Rh), ruthenium (Ru), titanium (Ti), thallium (Tl), thulium (Tm), tungsten (W), zirconium (Zr), magnesium (Mg), palladium (Pd), zinc (Zn), chromium (Cr), iron (Fe), platinum (Pt), scandium (Sc), tantalum (Ta), or combinations thereof.

In some embodiments disclosed NFTs can include ternary alloys that are made of a primary material and at least two secondary materials. In some embodiments disclosed NFTs can include one primary material selected from gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two secondary atoms selected from any of those listed herein.

While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples provided below.

EXAMPLES

An illustrative process flow for carrying out a disclosed method can include the following: deposition of a primary element (e.g., a plasmonic material such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), or a combination thereof) to form a primary element film or layer; definition of the peg of a NFT from the primary element film or layer using patterning methods such as photolithography for example; formation of the peg of a NFT using removal methods such as etching, etc.; encapsulation of the peg with a dielectric material; definition of an implant area using a mask; and implantation of a secondary element(s) in the implant area of the primary element film. In some embodiments, an optional heat treatment step can be carried out after the step of implanting the secondary element(s). In some embodiments, an optional step of removing at least part of the encapsulating dielectric material can be undertaken after implantation of the secondary element(s) (or optionally after the optional heat treatment). This can help control the interfacial and optical properties of the encapsulant film. If at least part of the encapsulating dielectric material was removed, another optional step may be added to redeposit some additional dielectric material (either the same dielectric material or a different dielectric material).

Another illustrative process flow for carrying out a disclosed method can include the following: deposition of a primary element (e.g., a plasmonic material such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), or a combination thereof) to form a primary element film or layer; implantation of a secondary element(s) in the primary element film to form a NFT layer; definition of the peg of a NFT from the NFT layer using patterning methods such as photolithography for example; formation of the peg of a NFT using removal methods such as etching, etc. In some embodiments, an optional step of deposition of a dielectric material on the primary element film or layer can be carried out before the secondary element(s) is implanted. In some embodiments, an optional heat treatment step can be carried out after the step of implanting the secondary element(s). In some embodiments, an optional step of removing at least part of the encapsulating dielectric material can be undertaken after implantation of the secondary element(s) (or optionally after the optional heat treatment). This can function to remove dielectric material that may have secondary element(s) implanted therein. If at least part of the encapsulating dielectric material was removed, another optional step may be added to redeposit some additional dielectric material (either the same dielectric material or a different dielectric material) once the peg is formed.

Another illustrative process flow for carrying out a disclosed method can include the following: deposition of a primary element (e.g., a plasmonic material such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), or a combination thereof) to form a primary element film or layer on a substrate that can contain other layers, structures, or both; definition of a plurality of pegs of NFTs from the primary element layer using patterning methods such as photolithography for example; formation of the plurality of pegs of the NFTs using removal methods such as etching, etc.; formation of a plurality of entire magnetic recording heads containing the pegs of the NFTs on the substrate; slicing the substrate into rows, each row containing a plurality of magnetic recording heads; forming at least a portion of an overcoat on the row; and implantation of a secondary element(s) in at least the peg regions of the primary element film to form alloyed NFTs. In some embodiments, an additional portion of the overcoat layer can be deposited after implantation of the at least one secondary element. In some embodiments a portion of the overcoat material may be advantageously removed and re-deposited to control the integrity and film stress of the head overcoat.

Ion implantation was carried out on a 25 nm sheet of film of NFT material. The NFT material can be deposited on top of the CNS and appropriate seed material. Illustrative specific implantation parameters can include the following. For carbon (C), an implant voltage of 6 keV, a dose of 1E14 ions/cm2 and 1E15 ions/cm2, and a wafer tilt angle of 0 degrees. For nitrogen (N), an implant voltage of 7.2 keV, a dose of 1E14 ions/cms and 1E15 ions/cm2, and a wafer tilt angle of 0 degrees. Following ion implantation the NFT film was patterned and formed into a NFT peg.

Ion implantation was carried out on a patterned NFT peg and heat sink which were encapsulated with 10 nm AlOx. Illustrative specific implantation parameters can include the following. For carbon (C), an implant voltage of 15 keV, a dose of 1E14 ions/cm2 and 1E15 ions/cm2, and a wafer tilt angle of 45 degrees. For nitrogen (N), an implant voltage of 18 keV, a dose of 1E14 ions/cms and 1E15 ions/cm2, and a wafer tilt angle of 45 degrees.

All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure.

As used in this specification and the appended claims, “top” and “bottom” (or other terms like “upper” and “lower”) are utilized strictly for relative descriptions and do not imply any overall orientation of the article in which the described element is located.

As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise.

As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. The term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements.

As used herein, “have”, “having”, “include”, “including”, “comprise”, “comprising” or the like are used in their open ended sense, and generally mean “including, but not limited to”. It will be understood that “consisting essentially of”, “consisting of”, and the like are subsumed in “comprising” and the like. For example, a conductive trace that “comprises” silver may be a conductive trace that “consists of” silver or that “consists essentially of” silver.

As used herein, “consisting essentially of,” as it relates to a composition, apparatus, system, method or the like, means that the components of the composition, apparatus, system, method or the like are limited to the enumerated components and any other components that do not materially affect the basic and novel characteristic(s) of the composition, apparatus, system, method or the like.

The words “preferred” and “preferably” refer to embodiments that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure, including the claims.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. or 10 or less includes 10, 9.4, 7.6, 5, 4.3, 2.9, 1.62, 0.3, etc.). Where a range of values is “up to” a particular value, that value is included within the range.

Use of “first,” “second,” etc. in the description above and the claims that follow is not intended to necessarily indicate that the enumerated number of objects are present. For example, a “second” substrate is merely intended to differentiate from another infusion device (such as a “first” substrate). Use of “first,” “second,” etc. in the description above and the claims that follow is also not necessarily intended to indicate that one comes earlier in time than the other.

Thus, embodiments of materials for near field transducers and near field transducers containing the same are disclosed. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present disclosure can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation. 

What is claimed is:
 1. A device comprising: a near field transducer, the near field transducer comprising gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two other secondary atoms, the at least two other secondary atoms selected from: boron (B), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), nitrogen (N), oxygen (O), carbon (C), gadolinium (Gd), samarium (Sm), thallium (Tl), cadmium (Cd), phosphorus (P), lead (Pb), hafnium (Hf), erbium (Er), zinc (Zn), magnesium (Mg), vanadium (V), zinc (Zn), chromium (Cr), lithium (Li), nickel (Ni), platinum (Pt), sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), beryllium (Be), thulium (Tm), erbium (Er), ytterbium (Yb), promethium (Pm), cerium (Ce), lanthanum (La), praseodymium (Pr), or combinations thereof.
 2. The device according to claim 1, wherein the NFT comprises about 0.1 atomic percent to about 50 atomic percent in total of the at least two secondary atoms.
 3. The device according to claim 1, wherein the NFT comprises about 0.1 atomic percent to about 5 atomic percent in total of the at least two secondary atoms.
 4. The apparatus according to claim 1 further comprising an energy source.
 5. The device according to claim 1, wherein the NFT comprises silver (Ag) and at least two other secondary atoms selected from: sodium (Na), thallium (Tl), lead (Pb), cesium (Cs), rubidium (Rb), beryllium (Be), boron (B), and manganese (Mn).
 6. The device according to claim 1, wherein the NFT comprises copper (Cu) and at least two other secondary atoms selected from: cadmium (Cd), indium (In), sodium (Na), thallium (Tl), cesium (Cs), rubidium (Rb), lead (Pb) and tin (Sn).
 7. The device according to claim 1, wherein the NFT comprises aluminum (Al) and at least two other secondary atoms selected from: boron (B), beryllium (Be), tin (Sn), indium (In), lead (Pb), thallium (Tl), sodium (Na), rubidium (Rb) and cesium (Cs).
 8. The device according to claim 1, wherein the NFT comprises gold (Au) and at least two other secondary atoms selected from: erbium (Er), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), zinc (Zn), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), gadolinium (Gd), germanium (Ge), hydrogen (H), iodine (I), osmium (Os), phosphorus (P), rubidium (Rb), selenium (Se), samarium (Sm), terbium (Tb), and thallium (Th).
 9. A device comprising: a light source; a waveguide; and a near field transducer, the near field transducer comprising gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two other secondary atoms, the at least two other secondary atoms selected from: boron (B), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), nitrogen (N), oxygen (O), carbon (C), gadolinium (Gd), samarium (Sm), thallium (Tl), cadmium (Cd), phosphorus (P), lead (Pb), hafnium (Hf), erbium (Er), zinc (Zn), magnesium (Mg), vanadium (V), zinc (Zn), chromium (Cr), lithium (Li), nickel (Ni), platinum (Pt), sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), beryllium (Be), thulium (Tm), erbium (Er), ytterbium (Yb), promethium (Pm), cerium (Ce), lanthanum (La), praseodymium (Pr), or combinations thereof.
 10. The device according to claim 9, wherein the NFT comprises about 0.1 atomic percent to about 50 atomic percent in total of the at least two secondary atoms.
 11. The device according to claim 9, wherein the NFT comprises about 0.1 atomic percent to about 5 atomic percent in total of the at least two secondary atoms.
 12. A disc drive comprising: at least one actuator arm having a first and a second end; at least one head, wherein each arm has a head at the first end thereof and wherein each head comprises: a light source; a near field transducer, the near field transducer comprising gold (Au), silver (Ag), copper (Cu), or aluminum (Al), and at least two other secondary atoms, the at least two other secondary atoms selected from: boron (B), indium (In), sulfur (S), silicon (Si), tin (Sn), manganese (Mn), tellurium (Te), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), germanium (Ge), hydrogen (H), iodine (I), rubidium (Rb), selenium (Se), terbium (Tb), nitrogen (N), oxygen (O), carbon (C), gadolinium (Gd), samarium (Sm), thallium (Tl), cadmium (Cd), phosphorus (P), lead (Pb), hafnium (Hf), erbium (Er), zinc (Zn), magnesium (Mg), vanadium (V), zinc (Zn), chromium (Cr), lithium (Li), nickel (Ni), platinum (Pt), sodium (Na), strontium (Sr), calcium (Ca), yttrium (Y), thorium (Th), beryllium (Be), thulium (Tm), erbium (Er), ytterbium (Yb), promethium (Pm), cerium (Ce), lanthanum (La), praseodymium (Pr), or combinations thereof; a magnetic reader; and a magnetic writer, wherein the light source and the near field transducer are configured to transmit light from the light source to the near field transducer in order to assist the magnetic writer with writing.
 13. The device according to claim 12, wherein the NFT comprises about 0.1 atomic percent to about 50 atomic percent in total of the at least two secondary atoms.
 14. The device according to claim 12, wherein the NFT comprises about 0.1 atomic percent to about 5 atomic percent in total of the at least two secondary atoms.
 15. The device according to claim 14, wherein the NFT comprises silver (Ag) and at least two other secondary atoms selected from: sodium (Na), thallium (Tl), lead (Pb), cesium (Cs), rubidium (Rb), beryllium (Be), boron (B), and manganese (Mn).
 16. The device according to claim 14, wherein the NFT comprises copper (Cu) and at least two other secondary atoms selected from: cadmium (Cd), indium (In), sodium (Na), thallium (Tl), cesium (Cs), rubidium (Rb), lead (Pb) and tin (Sn).
 17. The device according to claim 14, wherein the NFT comprises aluminum (Al) and at least two other secondary atoms selected from: boron (B), beryllium (Be), tin (Sn), indium (In), lead (Pb), thallium (Tl), sodium (Na), rubidium (Rb) and cesium (Cs).
 18. The device according to claim 14, wherein the NFT comprises gold (Au) and at least two other secondary atoms selected from: erbium (Er), holmium (Ho), lutetium (Lu), praseodymium (Pr), scandium (Sc), uranium (U), zinc (Zn), barium (Ba), chlorine (Cl), cesium (Cs), dysprosium (Dy), europium (Eu), fluorine (F), gadolinium (Gd), germanium (Ge), hydrogen (H), iodine (I), osmium (Os), phosphorus (P), rubidium (Rb), selenium (Se), samarium (Sm), terbium (Tb), and thallium (Th). 